The main function of the epidermis is to ensure a protective barrier between the external environment and the body. Skin, in direct contact with the external environment, is exposed to many changes in environmental conditions. Depending on the nature and extent of the changes, they can cause damage responsible for physical, chemical or biological stress. The main stresses are thermal stress, exposure to free radicals of oxygen, ultraviolet and infrared radiation, heavy metals, osmotic shock and pressure shock and also pathological conditions such as fever, inflammation, viral infection, etc.
Thermal stress is defined as stress affecting the body's optimal functioning and which exceeds the body's physiological thermoregulation mechanisms. Thermal stress is produced following a decrease (cold thermal stress) or an increase (hot thermal stress) in temperature, of environmental or internal origin. A deviation of a few degrees from this optimal temperature can have significant consequences.
Thermal shock is defined as stress caused by a sudden and significant temperature variation (temperature change of at least 10° C.).
Skin can be exposed to thermal stress in many physiological or accidental situations. The average skin temperature can be estimated as a constant value that is about 33° C. in optimal functioning, and can quickly change depending on exposure to the environment, for example it falls to 27° C. after immersion in a 24° C.-bath (Marino and Booth, 1998) and can rise beyond 37° C. following sun exposure.
Cold thermal stress can include deep hypothermia, in which the temperature of tissues and organs falls below 25° C. (such as exposure to extreme cold temperatures or else in certain medical techniques to protect the organs and tissues from hypoxia), and moderate hypothermia (temperature of between 25° C. and 35° C.) as in, for example, repeated exposure to air conditioning when moving between inside rooms and the outside every day in summer and winter, or else bathing.
The skin is frequently subjected to moderate cold thermal stress followed by successive warmings. The following are among the cellular physiological effects of exposure to cold (Fujita et al.):                Increased protein denaturation and disaggregation        Slowdown in progression through the cell cycle, the G1 phase generally being the most sensitive        Inhibition of transcription and translation, which leads to a general reduction in protein synthesis        Disruption in elements of the cellular cytoskeleton        Changes in membrane permeability which leads to increased cytosolic Na+ and H+ ions.        
In addition, repeated skin exposure to repeated temperature variations can cause harmful effects on cell phenotype or else on the structure and lipid compositions of cellular membranes, thus altering the barrier function of the skin and leading to irritation, dryness or else cracking. These effects due to temperature variations and cold thermal stress accelerate the aging process of the skin.
Resistance to thermal stress is enabled by the establishment of a specific cellular response. In the case of cold thermal stress, the cell establishes a protection system by inducing the transcription of a specific gene family that results in the synthesis and intracellular accumulation of cold shock proteins or “CSP,” these being different from heat shock proteins or “HSP.”
Among CSPs, Cold-inducible RNA-binding protein, or CIRBP, is a protein coded, in humans, by the CIRBP gene. These proteins are expressed constitutively as well as after exposure to cold. CIRBP plays a critical role in controlling cellular response to a variety of cellular stresses, including short wavelength ultraviolet light, hypoxia and hypothermia. Its expression rapidly and significantly increases during moderate hypothermia (Fujita et al., J. Mol. Microbiol. Biotechnol., 1999; Larry et al, J. Appl. Physiol., 2002) among the other roles of CIRBP:                Inhibition of RNA degradation        Increase in the transcription of specific target genes via elements from the promoter region of these genes,        Alternative splicing of pre-mRNA        
The special properties of CIRBPs make them interesting biological markers of the body's reaction to temperature shocks.
Extracts of Artemia salina are already used in cosmetics. For example, document FR 2 817 748 describes an Artemia salina extract for preventing skin aging due to UV damage, document FR 2 835 743 describes an Artemia salina extract for limiting the side effects of retinoids and application WO 1999038483 describes a cosmetic product based on Artemia salina extracts for the regeneration and stimulation of skin cells.
However, to date, no one has established a connection between an Artemia salina extract and the protection of skin from damage due to thermal stress.
The inventors have demonstrated that the application of an effective quantity of an Artemia salina extract enables cells to be protected from thermal stress that can cause skin damage, particularly cold thermal stress or repeated temperature variations.
The invention and resulting advantages will be better understood upon reading the description.